A number of fields have interest in epoxy materials, including for example the aero industry, space industry and automobile industry, or even in such fields as sport equipment manufacturing, adhesive and sealant manufacturing, wood products, coatings and manufacturing of components for pipes, boats and reservoirs, and transportation, train and space industries.
Since most epoxy resins for use in high temperature structural applications are brittle, a considerable amount of work has been undertaken in an attempt to enhance the toughness of these materials; moreover, over the years, efforts have been made to improve barrier resistance performance such as flammability resistance and water absorption resistance, of these materials. Typical toughening methods include the addition of a second phase such as rubber particles, thermoplastic particles or mineral fillers.
Polymer-layered silicate nanocomposites are another avenue, due to dramatic improvements in mechanical properties, barrier properties and thermal resistance at low clay loading observed in these materials as compared with a pristine matrix, i.e. with a polymer without clay.
It has been shown that organoclay may simultaneously improve both toughness and elastic modulus of epoxy resins in a more efficient way than fillers. Therefore, nanocomposite technology using organoclay as a nano-scale reinforcement offers an interesting alternative for modifying epoxy resins. Clay minerals are principally silicates of aluminium, iron, and magnesium and belong to the phyllosilicate (or layer silicate) family of minerals. Epoxies are usually thermosetting resins obtained by polymerisation of an epoxide, such as ethylene oxide or epichlorohydrin, especially with a diphenol.
The U.S. Pat. No. 4,465,797 by Brownscombe et al. describes a reinforced polymer composition comprising an epoxy resin matrix having intimately distributed therein a particulate or filamentary silicate or aluminosilicate mineral, in concentrations in the range from 10-30 phr (parts per hundred of resin by weight). A method for preparing such reinforced polymer composition comprises mixing the components into a liquid resin mixture, applying pressure thereto, forcing it through a ¾″ diameter line into a mold, and removing the pressure.
In the U.S. Pat. No. 5,840,796, Badescha et al. disclose a polymer nanocomposites comprising a mica-type layered silicate and having an exfoliated structure or an intercalated structure resulting from mechanical shear.
In European patent EP 0890616, Suzuki et al. describe an epoxy composite comprising sheet-like clay reinforcement for improving the mechanical strength. In U.S. Pat. No. 6,391,449, Lan et al. describe a method for fabricating polymer-clay intercalates exfoliates nanocomposites comprising preparing a mixture of at least two swellable matrix polymers and incorporating the mixture with a matrix polymer by melt processing the matrix polymer with the mixture. Barbee et al., in U.S. Pat. No. 6,384,121, contemplate producing a nanocomposite comprising an epoxy resin and layered clay material, by forming a concentrate of the clay material and melt compounding the concentrate with the epoxy matrix. Polansky et al. in U.S. Pat. No. 6,287,992 propose a polymer nanocomposite comprising an epoxy resin matrix having dispersed therein particles derived from a multilayered inorganic material, and having an increased fracture toughness and enhanced barrier properties against small molecules.
Knudson Jr. et al., in the published United States patent application US 2002/0165305, disclose a method for preparing polymer nanocomposites by mixing dispersions of polymers and dispersions of clay minerals. More precisely, the method comprises mixing a dispersion of thermoplastic polymers in a first liquid carrier with a dispersion of clay in a second liquid carrier, wherein the dispersion of thermoplastic polymers may be achieved by a shearing process, the dispersion of clay may be achieved in a high shear mixer of a Manton-Gaulin mill type (described in Knudson Jr. et al's U.S. Pat. No. 4,664,842), and the mixing of the two dispersions is achieved under sufficient shear, with addition of flocculating agent, or filtration, centrifugation and drying.
Lorah et al., in the published United States patent application US 2002/0055581, recently contemplated a method for producing improved epoxy nanocomposite characterised by a uniform dispersion of clay therein by enhancing the affinity between the clay and the polymer at the interface.
Layered silicate clay is seen as an ideal reinforcement for polymers due to its high aspect ratio, but untreated clay is not easily dispersed in most polymers because of its natural hydrophilicity and incompatibility with organic polymers.
The high-performance tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) epoxy resin and 4,4′-diaminodiphenyl sulphone (DDS) system is widely used as the matrix for advanced composites in military and civil aircraft due to its good comprehensive properties such as excellent adhesion with fiber, relatively high strength and stiffness at room and elevated temperatures, processing versatility and reasonable cost etc. However, this resin system is very brittle and flammable, and has a high equilibrium content of water absorption.
A hybrid approach of adding both fillers and rubbers to epoxy resins has also been studied. However, a high concentration of fillers results in the reduction of processability.
Therefore there appears to be still a need in the art for an improved method and system for making high-performance epoxies.